If descent is not possible, a portable hyperbaric chamber (Gamow bag) can be used to simulate a lower altitude.

The higher the altitude at which a hyperbaric chamber is used, the greater the apparent descent can be simulated. (This is because portable hyperbaric chambers can increase atmospheric pressure by 2 pounds per square inch.)

For example, a hyperbaric chamber at 9,800 feet (3,000 meters) can simulate a descent of 4,800 feet (1,500 meters), but the same hyperbaric chamber used at 24,600 feet (7,500 meters) can simulate a descent of 7,800 feet (2,400 meters).